Obtencao e caracterizacao de farinha de casca de uva e sua utilizacao em snack extrusado/Obtention and characterization of grape skin flour and its use in an extruded snack

This study aimed to characterize grape skin flour (GSF) and the effect of its inclusion in an extruded snack, with regard to the nutritional, technological and sensory parameters. Grape pomace from the cultivar Marselan (Vitis vinifera), obtained during the winemaking process, was used to obtain the grape skin flour. The in natura pomace was dried in a forced air oven at 55 degree C for 24 hours. The skins were separated from the seeds using 2 mm and 3 mm sieves, and the skins subsequently ground in a micro mill at 27.000 rpm (particles < 1 mm) and stored at -18 degree C. The grape skin flour obtained was submitted to a chemical analysis (moisture, ash, protein, lipids, total dietary fibre, carbohydrates, pH, phenolic compounds and colour). The GSF was included in the formulation of an extruded snack at levels of 9% and 18%, substituting the corn flour, representing 5% and 10% fibre, respectively. The snacks were evaluated for colour, texture and acceptance. A microbiological analysis for coliforms at 45 degree C and Salmonella was carried out on the test formulations. Fibre (58.01%), ash (12.46%) and carbohydrates (17.62%) were the main constituents of the grape skin flour, which had a pH value of 3.51. The phenolic compounds resveratrol (6.14 mg.g-1), luteolin (5.16 mg.g-1) and kaempferol (3.01 mg.g-1) were detected in the largest amounts in the GSF, indicating the presence of antioxidants in the flour. The snack containing 9% (5% fibre) of GSF showed the best results for acceptance with respect to the attributes of colour, aroma and texture as compared to the standard snack. The addition of GSF to extruded snacks is feasible and of interest due to its nutritional enrichment (fibre and phytochemicals) and aggregation of value to a byproduct discarded by wineries.